| ??? 01/10/09 09:50 Read: times |
#161403 - figure 1.4W Responding to: ???'s previous message |
Per Westermark said:
I don't know where you got the figure 1.4W from, but I think you read the datashseet wrong.
As long as the ambient temperature is no higher than 65C, you may power the chip in such a way that the total power loss may be up to 1.2W. But if the ambient temperature is higher than 65C, you must give the chip a lower supply voltage, because every degree higher ambient temperature requires you to reduce the power loss in the chip with 12mW. The reason is that at 65C ambient temperature, the chip will reach max allowed temperature at 1.2W power dissipation. With higher ambient temperature, it will take less power for the chip to reach max temperature. At 85C ambient temperature, the maximum allowed power dissipation in the chip is 1.2 - 20*0.012 W = 0.96W. This is similar to a normal resistor. It has a power rating that is valid up to a specified ambient temperature. But it also have a zero-power temperature where the ambient temperature is so high that you may not produce any internal warming of the resistor. Thanks , Actually I meant 1.2+20*0.12W =1.4W that it will begin to dissipate at that elevated temp unless any action is taken. Kai Klaas said:
On the other hand, temperature cycling by periodically turning the chip on and off will stress the chip even much more than a permanent higher die temperature! The only remedy is to find a cooler place for the chip and/or to decrease the heat dissipation by choosing a lower supply voltage and/or by cooling the chip in a suited way (fan, heat sink). But don't forget, that the AD598 is designed to be very reliable. Wafer tests at 55°C have shown a mean time between failure (MTBF) of 3,122,147,185 hours (60% confidence level). Using the Arrhenius equation again translates this to a MTBF of 393,067,365 hours at 85°C die temperature. So, at 85°C die temperature the MTBF is about 45000 years and at 133°C about 3100 years. Or by other words: After a life time of 10 years at 85°C die temperature you will observe about one of 4500 devices containing a damaged AD598, and one of 310 devices when running the AD598 at 133°C die temperature. I guess, when using power cycling, on the other hand, all will be damaged after 10 years...Kai Kai , Where did you get those MTBF figures I searched the site but couldnt find. I want a hint as to how this is done "Using the Arrhenius equation again translates this to a MTBF of 393,067,365 hours at 85°C die temperature"? -AP |
| Topic | Author | Date |
| Thermal stress reduction for IC | 01/01/70 00:00 | |
| Ask the manufacturer! | 01/01/70 00:00 | |
| Wear from temperature cycling | 01/01/70 00:00 | |
| loose vs lose | 01/01/70 00:00 | |
| What's the rated MTBF? | 01/01/70 00:00 | |
| The temperature may rise | 01/01/70 00:00 | |
| automotive grade is 125C | 01/01/70 00:00 | |
| You should have mentioned 150C | 01/01/70 00:00 | |
| Why does it rise? | 01/01/70 00:00 | |
| Though its able | 01/01/70 00:00 | |
| Sounds unlikely to me | 01/01/70 00:00 | |
| You need to consume power to be able to save power | 01/01/70 00:00 | |
| Why not having some numbers? | 01/01/70 00:00 | |
| Power dissipation | 01/01/70 00:00 | |
| Not 1.4W at 85C but 1.2-0.24 = 0.96W | 01/01/70 00:00 | |
| figure 1.4W | 01/01/70 00:00 | |
| Reversed logic | 01/01/70 00:00 | |
| Agreed | 01/01/70 00:00 | |
| Answers | 01/01/70 00:00 | |
| The webpage accepts | 01/01/70 00:00 | |
| Useful links... | 01/01/70 00:00 | |
| Tjmax | 01/01/70 00:00 | |
| Please read the datasheet again, carefully! | 01/01/70 00:00 | |
Not Obsession only info | 01/01/70 00:00 |